| HC pollutant from vehicle emissions was an important source of VOC emissions in the air.With the vehicle exhaust emission regulations constantly tightened,the proportion of HC from exhaust emission gradually decreased,but HC from evaporative emission was bigger and bigger.Since China has been using the European emissions system,refueling emission test was not ever required.Little research had been done on refueling emission test in China,and the ORVR technology was almost a blank in China.In 2016,China issued a new emission regulation “China VI” for light duty vehicles,refueling emission test was added to control HC from refueling.In this paper,the refueling emissions tests were implemented on gasoline vehicles with SHED,under different test conditions.Firstly,formation of refueling emission was theoretically analysed,and main structure characteristics and working principle of ORVR system were analysed in detail.Secondly,the development of control technology for refueling emission was reviewed,and the test plan for refueling emission test in this study was made,according to the regulations of the United States on the vehicle emission test.Then,the recovery efficiency of the ORVR system was studied,and the effects of different refueling rate,fuel temperature and preconditioning driving cycles on the refueling test results were analyzed.Finally,the refueling emission factors were calculated from the experiment results,and the total annual refueling emission was calculated.The main study results are as follows:(1)Two same type groups of Chinese and American vehicles were selected to analys vapor recovery efficiency of ORVR.The refueling test results of Chinese SUV was 0.834g/L,vapor recovery efficiency was only 0.21%.Two refueling test results of American SUV were 0.0051g/L and 0.0049g/L,the average vapor recovery efficiency reached 99.485%.The refueling test results of Chinese saloon was 0.724g/L,vapor recovery efficiency was 1.51%.And two refueling test results of American saloon car were 0.0029g/L and 0.0031g/L,the average vapor recovery efficiency reached 99.685%.For same type vehicles,vehicles equipped with ORVR system could effectively control the emission of HC during refueling.(2)The American SUV and saloon were chosen for refueling emission tests at different refueling rate.From 30L/min to 37L/min,the refueling emission results showed a decreasing trend;as 37L/min to 45L/min,the refueling emissions remained unchanged.The refueling emissions of American SUV and saloon car at 30L/min were 1.22 times and 1.48 times at standard condition.When refueling rate low,it was not conducive to the formation of liquid seal in filler pipe,and tank internal pressure increased slowly,which increased the probability of vapor overflow from fuel inlet;when refueling rate too fast,there may be a risk of anti spray and splash.Recommended that the refueling rate maintained at 37L/min.(3)The American SUV and saloon were chosen for refueling emission tests at different.fuel temperature.It showed that,as the increase of fuel temperature,the refueling emission was increasing,and the higher the temperature,the faster the increase of refueling emission.From 15? to 22?,the refueling emissions difference of American SUV on adjacent temperature range were only 11.63%,8.33% and 11.54%,the American saloon car's emission difference were 15%,17.65% and 17.39%.When the fuel temperature from 22? increased to 25?,refueling emissions increased sharply.The American SUV and saloon car emissions increased by 56.90% and 114.81%.Gasoline had a strong volatile characteristics,the temperature higher,the gasoline molecular thermal motion intenser,more easily volatilized to form vapor.The fuel temperature should be controlled as much as possible at 20? when refueling.(4)An American SUV was conducted 3 refueling emission tests,under diffierent purge preconditioning cycles.The average total purge flow of FTP 75 driving cycles and WLTC combination cycles was 987.56 L and 875.33 L,respectively.The total purge flow of FTP 75 was 1.13 times of WLTC,so FTP75 cycle had a better desorption effect.The refueling test results of EPA were 0.0331g/L,0.0367g/L,0.0396g/L,meeting the limit requirement of 0.053g/L.The results of China VI were 0.111g/L,0.103g/L,0.107g/L,which was about 3 times of EPA results.The larger the purge flow of carbon canister was,the more the desorption was,the better control effect of the refueling emission was.For different desorption driving cycles,the carbon canister desorption calibration should be pointedly carried out.(5)12 Chinese and Amerian vehicles were selected respectively,which meeting request of China V and Tier II.The refueling emission factor derived from laboratory test with SHED for Chinese vehicles was 0.78349g/L,which was about 60% of the factor 1.32g/L released by EPA.And the refueling emission factor for American vehicles was only 0.00872g/L.Taking Beijing as an example,single vehicle annual total refueling emission for regular gasoline car was 1204.789g/year/vehicle,for car with ORVR was only 13.394 g/year/vehicle.Considering all gas station with Stage II,single vehicle annual total refueling emission for regular gasoline car was still 381.437g/year/vehicle,which was still about 27 times of vehicles with ORVR.Installation of ORVR systems could reduce refueling emissions by 96% per year. |
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